This chapter is from the book

Radio
frequency
identification (RFID)
technology
uses
radio
waves
to
automatically
identify
physical
objects
(either
living
beings
or
inanimate
items).
Therefore,
the
range
of
objects
identifiable
using
RFID
includes
virtually
everything
on
this
planet
(and
beyond).
Thus,
RFID
is
an
example
of automatic
identification (Auto-ID)
technology
by
which
a
physical
object
can
be
identified
automatically.
Other
examples
of
Auto-ID
include
bar
code,
biometric
(for
example,
using
fingerprint
and
retina
scan),
voice
identification,
and optical
character
recognition (OCR)
systems.

Consider
the
word identify more
closely.
Although
two
cans,
A and
B, of
a particular
brand
of motor
oil
in a
store
might
look
identical,
substantial
differences
between
the
two
might
in fact
exist.
For
example,

The
retailer might have used two different
order numbers to obtain cans A
and B from the distributor.

Can
A might have been produced in
North America, whereas can B might
have been manufactured in Asia.

A
person named Bob might have loaded
A onto the delivery truck, whereas
a person named Chi might have
loaded B onto a similar truck.

Can
A might have arrived in the store
on a different date than when
can B arrived.

Generally,
although
none
of the
preceding
information
appears
on cans
A or
B for
a person
to view
in a
store,
this
information
is nonetheless
associated
with
these
cans.
You
can,
by using
a set
of such
information,
uniquely
identify
can
A from
can
B. Also,
even
assuming
that
no such
information
exists,
the
very
fact
that
that
two
distinct
physical
objects
exist
suggests
the
possibility
to distinguish
them
(for
example,
by assigning
a number
that
is unique
to can
A and
one
that
is unique
to can
B).
In summary,
although
cans
A and
B might
look
identical
in appearance,
composition,
expiration
date,
recycling
information,
and
so on,
they
can
actually
be differentiated
in some
way
so that
cans
A and
B, and
any
other
can
of motor
oil
produced
by this
particular
manufacturer
(or
any
other
manufacturer),
are unique
in some
way.
When
used
in the
context
of RFID,
the
word identify refers
to this
uniqueness
of an
object.

The
implications
regarding
object
identity
are
tremendous.
For
example,
consider
how
the
preceding
example
of motor
oil
can
be extended
to other
objects,
irrespective
of whether
RFID
technology
can
be used
with:

Every
grain of rice consumed annually
worldwide

Every
grain of sand on every beach worldwide

Every
leaf on every tree worldwide

Every
drop of rain that falls worldwide
in a given year

The
objects
in this
preceding
list
represent potential identification
scenarios.
Current
RFID
technology
cannot
be used
to identify
these
objects.
Even
with
technological
advances
(over
the
next
10 years,
for
example),
some
(or
all)
of these
identification
scenarios
are
unlikely.
After
all,
how
can
you
tag
a raindrop,
which
has
an extremely
short
life
and
dynamic
behavior
(such
as dividing
into
smaller
raindrops
when
it grows
beyond
5 mm
in size)?

Before
delving
into
a detailed
discussion
of RFID
technology,
you
need
to understand
the
fundamental
terms
and
concepts
associated
with
RFID.
The
following
section
serves
as an
RFID
technology
primer.

1.1
Fundamental
Concepts

A wave is a disturbance that transports energy from one point to
another.

Electromagnetic waves are created by electrons in motion and consist
of oscillating electric and magnetic fields. These waves can pass through a
number of different material types.

The highest point of a wave is called a crest, and the lowest point
is called a trough.

The distance between two consecutive crests or two consecutive troughs is
called the wavelength.

One complete wavelength of oscillation of a wave is called a cycle.

The time taken by a wave to complete one cycle is called its period of
oscillation.

The number of cycles in a second is called the frequency of the
wave. The frequency of a wave is measured in hertz (abbreviated as Hz)
and named in honor of the German physicist Heinrich Rudolf Hertz. If the
frequency of a wave is 1 Hz, it means that the wave is oscillating at the rate
of one cycle per second. It is common to express frequency in KHz (or kilohertz
= 1,000 Hz), MHz (or megahertz = 1,000,000 Hz), or GHz (or gigahertz =
1,000,000,000 Hz).

Amplitude is the height of a crest or the depth of a trough from the
undisturbed position. The former is also called the positive amplitude,
and the latter the negative amplitude. In general, the amplitude at
a certain point of a wave is its height or depth from the undisturbed
position, and is called positive or negative accordingly.

Radio or radio frequency (RF) waves are
electromagnetic waves with wavelengths between 0.1 cm and 1,000 km. Another
equivalent definition in terms of frequency is radio waves are electromagnetic
waves whose frequencies lie between 30 Hz and 300 GHz. Other electromagnetic
wave types are infrared, visible light wave, ultraviolet, gamma-ray, x-ray, and
cosmic-ray.

RFID uses radio waves that are generally between the frequencies of 30 KHz
and 5.8 GHz.

A continuous wave (CW) is a radio wave with constant frequency and
amplitude. From a communications vantage, a CW does not have any embedded
information in it but can be modulated to transmit a signal.

Modulation refers to the process of changing the characteristics of
a radio wave to encode some information-bearing signal. Modulation can also
refer to the result of applying the modulation process to a radio wave.

Radio waves can be affected by the material through which they propagate. A
material is called RF-lucent or RF-friendly for a certain
frequency if it lets radio waves at this frequency pass through it without any
substantial loss of energy. A material is called RF-opaque if it
blocks, reflects, and scatters RF waves. A material can allow the radio waves to
propagate through it but with substantial loss of energy. These types of
materials are referred to as RF-absorbent. The RF-absorbent or
RF-opaque property of a material is relative, because it depends on the
frequency. That is, a material that is RF-opaque at a certain frequency could be
RF-lucent at a different frequency. The RF properties of some example materials
are provided in Table 1-2, following a discussion of RFID frequency types.

Classes of RFID frequency types include the following:

Low frequency (LF)

High frequency (HF)

Ultra high frequency (UHF)

Microwave frequency

The following subsections discuss these frequency types.

1.1.1 Low Frequency (LF)

Frequencies between 30 KHz and 300 KHz are considered low, and RFID systems
commonly use the 125 KHz to 134 KHz frequency range. A typical LF RFID system
operates at 125 KHz or 134.2 KHz. RFID systems operating at LF generally use
passive tags (discussed in Section 1.2.1), have low data-transfer rates from the
tag to the reader, and are especially good if the operating environment contains
metals, liquids, dirt, snow, or mud (a very important characteristic of LF
systems). Active LF tags (discussed in Section 1.2.1) are also available from
vendors. Because of the maturity of this type of tag, LF tag systems probably
have the largest installed base. The LF range is accepted worldwide.

1.1.2 High Frequency (HF)

HF ranges from 3 MHz to 30 MHz, with 13.56 MHz being the typical frequency
used for HF RFID systems. A typical HF RFID system uses passive tags, has a slow
data-transfer rate from the tag to the reader, and offers fair performance in
the presence of metals and liquids. HF systems are also widely used, especially
in hospitals (where it does not interfere with the existing equipment). The HF
frequency range is accepted worldwide.

The next frequency range is called very high frequency (VHF) and
lies between 30 and 300 MHz. Unfortunately, none of the current RFID systems
operate in this range. Therefore, this frequency type is not discussed any
further.

1.1.3 Ultra High Frequency (UHF)

UHF ranges from 300 MHz to 1 GHz. A typical passive UHF RFID system operates
at 915 MHz in the United States and at 868 MHz in Europe. A typical active UHF
RFID system operates at 315 MHz and 433 MHz. A UHF system can therefore use both
active and passive tags and has a fast data-transfer rate between the tag and
the reader, but performs poorly in the presence of metals and liquids
(not true, however, in the cases of low UHF frequencies such as 315 MHz
and 433 MHz). UHF RFID systems have started being deployed widely because of the
recent RFID mandates of several large private and public enterprises, such as
several international and national retailers, the U.S. Department of Defense,
and so on (see Chapter 10, "Standards"). The UHF range is not
accepted worldwide.

1.1.4 Microwave Frequency

Microwave frequency ranges upward from 1 GHz. A typical microwave RFID system
operates either at 2.45 GHz or 5.8 GHz, although the former is more common, can
use both semi-active and passive tags, has the fastest data-transfer rate
between the tag and the reader, and performs very poorly in the presence of
metals and liquids. Because antenna length is inversely proportional to the
frequency (see Section 1.2.1.1.2), the antenna of a passive tag operating in the
microwave range has the smallest length (which results in a small tag size
because the tag microchip can also be made very small). The 2.4 GHz frequency
range is called Industry, Scientific, and Medical (ISM) band and is
accepted worldwide.

International restrictions apply to the frequencies that RFID can use.
Therefore, some of the previously discussed frequencies might not be valid
worldwide. Table 1-1 lists some example frequency-use restrictions for RFID
together with the maximum allowable power and duty cycle
(explained later in this chapter).

Radio waves are susceptible to interference from various
sources, such as the following:

Weather conditions such as rain, snow, and other types of precipitation.
However, as mentioned before, these are not an issue at LF and HF.

The presence of other radio sources such as cell phones, mobile radios, and
so on.

Electrostatic discharge (ESD). ESD is a sudden flow of electrical
current through a material that is an insulator under normal circumstances. If a
large potential difference exists between the two points on the material, the
atoms between these two points can become charged and conduct electric
current.

The discussion now turns to how RFID technology works.

A radio device called a tag is attached to the object that needs to
be identified. Unique identification data about this tagged object is stored on
this tag. When such a tagged object is presented in front of a suitable RFID
reader, the tag transmits this data to the reader (via the reader antenna). The
reader then reads the data and has the capability to forward it over suitable
communication channels, such as a network or a serial connection, to a software
application running on a computer. This application can then use this unique
data to identify the object presented to the reader. It can then perform a
variety of actions such as updating the location information of this object in
the database, sending an alert to the floor personnel, or completely ignoring it
(if a duplicate read, for example).

As you can understand from this description, RFID is also a
data-collection technology. However, this technology has some unique
characteristics that enable users to apply it in areas beyond the reach of
traditional data-collection technologies, such as bar codes.

An RFID application is implemented by an RFID system, which constitutes the
entire technology end-to-end.